ION-SELECTIVE ELECTRODES BASED ON 2 COMPETITIVE IONOPHORES FOR DETERMINING EFFECTIVE STABILITY-CONSTANTS OF ION-CARRIER COMPLEXES IN SOLVENT POLYMER MEMBRANES

A new potentiometric method to determine effective complex formation c onstants in organic membrane phases is reported in detail, It demands measurements with two different membranes,one containing a highly sele ctive reference ionophore (in this case for H+) and anionic sites and another containing the same components and additionally the lipophilic ionophore to be characterized, The response characteristics of both e lectrodes can be compared and related to the effective complex formati on constant of the ion carrier in the membrane, Potentiometric experim ents with membranes containing a series of highly selective H+-ionopho res confirm that alkali metal ions are not complexed by these ionophor es. The ionophores valinomycin, BME-44, ETH 2120, tert-butylcalix-[4]a rene tetraethyl ester, and ETH 1810 are characterized using this poten tiometric technique with potassium, sodium, and lithium ions in the sa mple, The complex formation constants are generally large and correspo nd very well to data obtained with a previously established optical me thod.